1. Field of the Invention
The invention relates to a method for operating a fuel injection system of an internal combustion engine, having a high-pressure fuel pump that has a plurality of pump elements, having a metering valve disposed on the intake side of the high-pressure fuel pump, wherein the fuel quantity aspirated by the pump elements is controllable or regulatable by the metering valve, having a common rail, and having a pressure regulating valve; the pressure in the common rail is controlled or regulated by the pressure regulating valve.
2. Description of the Prior Art
Regulating the pumping quantity of high-pressure fuel pumps is of major significance for the overall efficiency of the fuel injection system of internal combustion engines and hence also for the engine fuel consumption. Furthermore, a high-pressure fuel pump whose pumping quantity can be regulated only to a limited extent must have greater reserves by design, which increases the production costs for the high-pressure fuel pump.
It is known from the prior art to limit the fuel quantity aspirated by the pump elements by means of a metering valve on the intake side of the pump elements and thus also to limit the pumping quantity of the high-pressure fuel pump. The pressure in the common rail is regulated by a pressure regulating valve, which as a rule is disposed on the common rail, or by a metering valve.
If the high-pressure fuel pump has a plurality of pump elements and the pumping quantity of the high-pressure fuel pump is reduced sharply by the metering valve, the result is an unequal distribution of the pumping quantity to the pump elements. For instance, it can happen that only two pump elements out of three make a significant contribution to pumping fuel, while a third pump element is de facto out of operation. This effect is unwanted, since it leads to increased pressure fluctuations in the common rail, and furthermore the performance required to drive the high-pressure fuel pump is also subject to major fluctuations. These performance fluctuations, like the aforementioned pressure fluctuations in the common rail, lead to nonconcentric operation of the engine in the partial-load range, and especially in idling.
The method of the invention provides that the fuel quantity flowing through the metering valve is detected; the theoretical pumping volume of the high-pressure fuel pump is detected or calculated; and the pressure regulating valve, if the fuel quantity pumped is less than a predetermined minimum pumping quantity, is triggered such that a defined leakage occurs.